1. Field of the Invention
This invention relates to a shield machine, and more particularly to an excavated earth and sand transporting apparatus for use in an earth pressure type shield machine by which much consisting of a mixture of excavated earth and sand, gravel, water etc. is carried to rearward of the shield machine and removed therefrom.
2. Description of the Prior Art
Conventional earth pressure type excavated earth and sand transporting apparatuses for use in shield machines are constructed such that one end of a screw conveyor is disposed inside a cutter head chamber mounted on the most front part of the shield proper, and the muck consisting of a mixture of excavated earth and sand, gravel and water etc. is carried by the screw conveyor to rearward of the shield proper. The arrangement is made such that, during the transportation of the muck, the amount of earth to be removed is restricted by gate means mounted on the rear end of the screw conveyor, and the resultant consolidation provides formation of a plug zone, which can resist the earth pressure and water pressure exerted on the face of a tunnel, inside the screw conveyor so that the excavated earth and sand may be conveyed to the outside in the form of a muck while the face is kept in a stable condition.
In such conventional apparatuses, however, it has been very difficult to regulate the degree of opening of the gate of the gate of the gate means in response to changes in the nature of soil in the natural ground to be excavated, the earth pressure, water pressure and the amount of water, and in consequence accidents such as spouting of the earth and sand and water have occurred frequently.
To eliminate this disadvantage, there have been employed a method of injecting a bentonite slurry and/or a clay slurry into the cutter head chamber or onto the front surface of the tunnel being excavated to form an impermeable layer inside the cutter head chamber or inside the screw conveyor thereby preventing spouting of spring water or a method of installing a rotary feeder behind the gate means of the screw conveyor so as to remove the excavated muck divided into sections or the like.
However, the above-mentioned method of injecting the bentonite slurry and/or clay slurry not only renders the cost expensive, but also gives naturally a limit in the capacity of the pump to supply slip agent or drilling mud of such a high concentration enough to prevent spouting of spring water, in particular, in dead water containing gravel layers. And also, because of the high concentration of the slip agent and/or drilling mud which are liable to stick, such a phenomenon as blocking of the cutter head and the screw conveyor occurred frequently. Further, in case the concentration of such fluids was reduced, it became naturally impossible to form a plug zone capable of preventing spouting of spring water, and therefore such a disadvantage as spouting-out of the earth and sand and ground water took place.
Whilst, in dead water containing gravel layers, if and when a rotary feeder is installed behind the gate means of the screw conveyor, the size of the rotary feeder suitable for the sizes of the gravels to be removed by the screw conveyor becomes big, and as a result, such a disadvantage as difficulty in bringing-in and assembly operation of segments and scattering of the muck removed from the rotary feeder thus rendering it impossible to load the muck on the belt conveyor which is the subsequent transport means which results in contamination of the tunnel pit being excavated took place.